For many years infusion packets, such as tea bags, were available primarily as square or round two-ply sheets of porous filter material with the infusible material, such as tea, sandwiched between the sheets. Such packets restrict the flow of infusible material within the packet substantially to two dimensions. As a result the infusion performance of such packets is limited.
Thus the past few decades have seen the development of mass-produced infusion packets which have a more three-dimensional shape and which allow the infusible substance more room to move. Of particular success have been the tetrahedral-shaped packets such as those described in the international patent applications published as WO 95/01907 (Unilever) and WO 2004/033303 (I.M.A. SPA).
In the manufacture of tetrahedral packets, the tetrahedral shape is conventionally formed by making mutually perpendicular transverse seals in a tube of filter material and apparatus designed for such manufacture is ill-suited to the manufacture of other three-dimensional shapes. Furthermore, although filling of the infusible material into the tubular packets at the high rates required for commercial mass-production is possible for readily-flowable and robust material such as finely-cut tea, delicate and/or sticky materials (such as large-leaf teas, fruit pieces and the like) often become damaged at the high dosing speeds.
It would, of course, be possible to operate at slower dosing speeds and yet produce tetrahedral infusion packages at high rates if several production lines were run in parallel but this would necessarily increase the cost and size of the manufacturing facilities required.
A process which is capable of producing such packets at a high speed without damaging such delicate materials would therefore be highly desirable.